Bottom Line:
Here, proteins must be folded and often further delivered across the matrix of the cell wall.PrsA2 is a member of a family of membrane-associated lipoproteins that contribute to the folding and stability of secreted proteins as they cross the bacterial membrane.PrsA2 contributes to the integrity of the L. monocytogenes cell wall as well as swimming motility and bacterial resistance to osmotic stress; however its most critical role may be its requirement for L. monocytogenes virulence and viability within host cells.

Affiliation: Department of Microbiology and Immunology, University of Illinois at Chicago Chicago, IL, USA.

ABSTRACTIn Gram-positive bacteria, the secretion of proteins requires translocation of polypeptides across the bacterial membrane into the highly charged environment of the membrane-cell wall interface. Here, proteins must be folded and often further delivered across the matrix of the cell wall. While many aspects of protein secretion have been well studied in Gram-negative bacteria which possess both an inner and outer membrane, generally less attention has been given to the mechanics of protein secretion across the single cell membrane of Gram-positive bacteria. In this review, we focus on the role of a post-translocation secretion chaperone in Listeria monocytogenes known as PrsA2, and compare what is known regarding PrsA2 with PrsA homologs in other Gram-positive bacteria. PrsA2 is a member of a family of membrane-associated lipoproteins that contribute to the folding and stability of secreted proteins as they cross the bacterial membrane. PrsA2 contributes to the integrity of the L. monocytogenes cell wall as well as swimming motility and bacterial resistance to osmotic stress; however its most critical role may be its requirement for L. monocytogenes virulence and viability within host cells. A better understanding of the role of PrsA2 and PrsA-like homologs will provide insight into the dynamics of protein folding and stability in Gram-positive bacteria and may result in new strategies for optimizing protein secretion as well as inhibiting the production of virulence factors.

Figure 1: The evolutionary relationship of PrsA homologs from Gram positive bacteria. Shown is a phylogenetic tree of PrsA homologs from Listeria monocytogenes and other Gram positive bacteria created by CLUSTAL analysis. The scale bar indicates 1 substitution for every 10 nucleic acid residues.

Mentions:
Given the critical requirement of PrsA2 for L. monocytogenes pathogenesis, how does it functionally compare with homologs expressed in other Gram-positive bacteria? prsA-like genes can be identified based on encoded amino acid sequence homology in many Gram-positive bacterial species (Figure 1). Thus far, the proteins have been best characterized in L. monocytogenes and Bacillus subtilis, although relatively little is still known about their molecular function. Interestingly, not all Gram-positive bacteria have the same number of PrsA-like proteins (Figure 2). L. monocytogenes has two, PrsA1 and PrsA2. As mentioned above, the function of L. monocytogenes PrsA1 has yet to be determined as deletion of the gene has yielded no discernable phenotype (Alonzo et al., 2009, 2011; Alonzo and Freitag, 2010). The expression of prsA1 from the prsA2 promoter does not complement a prsA2 deletion, indicating that the lack of functional complementation observed was not due to differences in the timing of gene expression (Alonzo and Freitag, 2010). Streptococcus pyogenes, similar to L. monocytogenes, has two prsA alleles that also appear to encode proteins with non-redundant functions (Ma et al., 2006), whereas the related Streptococcal species Streptococcus pneumonia and Streptococcus mutans have only one prsA allele (Drouault et al., 2002; Guo et al., 2013). B. subtilis contains one prsA gene that was at first considered essential for viability but has recently been shown to be non-essential in the presence of high concentrations of magnesium (Hyyrylainen et al., 2010). In contrast, Bacillus anthracis has three prsA alleles that can complement B. subtilis PrsA, however whether one or more of these alleles are essential for B. anthracis viability is unknown (Williams et al., 2003). The single prsA alleles of S. mutans, Staphylococcus aureus, and Lactococcus lactis have been shown to be non-essential (Drouault et al., 2002; Jousselin et al., 2012; Guo et al., 2013).

Figure 1: The evolutionary relationship of PrsA homologs from Gram positive bacteria. Shown is a phylogenetic tree of PrsA homologs from Listeria monocytogenes and other Gram positive bacteria created by CLUSTAL analysis. The scale bar indicates 1 substitution for every 10 nucleic acid residues.

Mentions:
Given the critical requirement of PrsA2 for L. monocytogenes pathogenesis, how does it functionally compare with homologs expressed in other Gram-positive bacteria? prsA-like genes can be identified based on encoded amino acid sequence homology in many Gram-positive bacterial species (Figure 1). Thus far, the proteins have been best characterized in L. monocytogenes and Bacillus subtilis, although relatively little is still known about their molecular function. Interestingly, not all Gram-positive bacteria have the same number of PrsA-like proteins (Figure 2). L. monocytogenes has two, PrsA1 and PrsA2. As mentioned above, the function of L. monocytogenes PrsA1 has yet to be determined as deletion of the gene has yielded no discernable phenotype (Alonzo et al., 2009, 2011; Alonzo and Freitag, 2010). The expression of prsA1 from the prsA2 promoter does not complement a prsA2 deletion, indicating that the lack of functional complementation observed was not due to differences in the timing of gene expression (Alonzo and Freitag, 2010). Streptococcus pyogenes, similar to L. monocytogenes, has two prsA alleles that also appear to encode proteins with non-redundant functions (Ma et al., 2006), whereas the related Streptococcal species Streptococcus pneumonia and Streptococcus mutans have only one prsA allele (Drouault et al., 2002; Guo et al., 2013). B. subtilis contains one prsA gene that was at first considered essential for viability but has recently been shown to be non-essential in the presence of high concentrations of magnesium (Hyyrylainen et al., 2010). In contrast, Bacillus anthracis has three prsA alleles that can complement B. subtilis PrsA, however whether one or more of these alleles are essential for B. anthracis viability is unknown (Williams et al., 2003). The single prsA alleles of S. mutans, Staphylococcus aureus, and Lactococcus lactis have been shown to be non-essential (Drouault et al., 2002; Jousselin et al., 2012; Guo et al., 2013).

Bottom Line:
Here, proteins must be folded and often further delivered across the matrix of the cell wall.PrsA2 is a member of a family of membrane-associated lipoproteins that contribute to the folding and stability of secreted proteins as they cross the bacterial membrane.PrsA2 contributes to the integrity of the L. monocytogenes cell wall as well as swimming motility and bacterial resistance to osmotic stress; however its most critical role may be its requirement for L. monocytogenes virulence and viability within host cells.

Affiliation:
Department of Microbiology and Immunology, University of Illinois at Chicago Chicago, IL, USA.

ABSTRACTIn Gram-positive bacteria, the secretion of proteins requires translocation of polypeptides across the bacterial membrane into the highly charged environment of the membrane-cell wall interface. Here, proteins must be folded and often further delivered across the matrix of the cell wall. While many aspects of protein secretion have been well studied in Gram-negative bacteria which possess both an inner and outer membrane, generally less attention has been given to the mechanics of protein secretion across the single cell membrane of Gram-positive bacteria. In this review, we focus on the role of a post-translocation secretion chaperone in Listeria monocytogenes known as PrsA2, and compare what is known regarding PrsA2 with PrsA homologs in other Gram-positive bacteria. PrsA2 is a member of a family of membrane-associated lipoproteins that contribute to the folding and stability of secreted proteins as they cross the bacterial membrane. PrsA2 contributes to the integrity of the L. monocytogenes cell wall as well as swimming motility and bacterial resistance to osmotic stress; however its most critical role may be its requirement for L. monocytogenes virulence and viability within host cells. A better understanding of the role of PrsA2 and PrsA-like homologs will provide insight into the dynamics of protein folding and stability in Gram-positive bacteria and may result in new strategies for optimizing protein secretion as well as inhibiting the production of virulence factors.